1. Field of the Invention
This invention relates to a color printing technology employing a plurality of ink.
2. Description of the Related Art
In recent years, color inkjet printers have become widely used as image output apparatuses. An ordinary color inkjet printer uses multiple colors of ink, including the colors cyan (C), magenta (M) and yellow (Y) in addition to black (K). Any desired colors in a color image can be reproduced using these multiple types of ink.
In this type of printer, the amount of each type of usable ink that will be used is determined in accordance with the desired color in the color image. In this Specification, the process by which the amount of each ink used in order to reproduce a color during printing is termed “color separation” or “ink color separation”. The relationship between the color data for the color image and the amount of each color ink is stored beforehand in a color conversion lookup table (hereinafter “LUT”), and during printing, the amount of ink output is determined for each color ink for each pixel position with reference to the LUT. (See, for example, JP10-191089A.)
Color reproduction by the printer is determined based on the types of ink usable by the printer. Typically, any desired colors can be reproduced by combining three chromatic primary color inks (such as cyan (C), magenta (M) and yellow (Y), for example). In some cases, spot color inks having a hue different from any of these chromatic primary color inks may be used. Here, “spot color” means a color that can be separated into two chromatic primary color components. When spot color inks are used, color reproducibility can be improved for image areas having a hue that is close to any of the colors of the spot color inks. However, where both the chromatic primary and spot color inks described above are available, color separation processing that seeks to minimize the use of the spot color inks has not been incorporated into the conventional art.